MissingNo.

In the early days of Red and Blue it was discovered that a strange Pokemon not listed in any official media could be obtained in the red and blue versions--without even using a cheat device. This caused many speculations and rumors as to what this Pokemon really was and why it was present in the games. Some deemed it the "4th mystical bird" or a "virus" put in the game to prevent people from cheating. Others suspected that there were some Pokemon (the Pokegods) that were in early versions of the game but removed later. However the most widely accepted belief was (and still is) that it is simply a glitch.

**It has come to my attention that a particular site has ripped off (intentional or not) an FAQ written by my friend, MajinBlueDragon, which was used with permission on this site. To prevent people from thinking I was the one who stole it, I have re-written most of it though there still may be a few sentences that are word for word.
My point is: I do not steal my information, so do not e-mail me saying that I did.

This is the MissingNo. that started it all. It is unknown to me where the "classic" method of encountering MissingNo. originated, but it is probably safe to say that it came from Nintendo's [official] Pokemon forums back in 98 or early 99.

Since there are multiple ways of obtaining MissingNo., I will be referring to this one (being the original) as the "classic" method.

In order to do this you will need:
a Pokemon with SURF
a Pokemon with FLY (not really needed but it makes things a lot easier)

First, talk to the old man in Viridian City who catches weedle. Tell him that you are not in a hurry and watch him catch it. Immediately after that, go to (I recommend you FLY there, though you can SURF and it will still work) Cinnabar Island and SURF on the 'half land half water' parts around the island.
Only SURF on those parts and you should eventually run into:
MissingNo.
M
A (non glitched) Pokemon that you normally wouldn't see in that area
some combination of the three.

No matter which combination of Pokemon you get, they will always either be on level 80 or a level above 100. When a glitch Pokemon is captured using this method, it will almost always revert to level 100 after getting any experience points.

When using the "classic" method of encountering MissingNo., another Pokemon that looks identical to MissingNo. but with a different cry may also appear. This Pokemon is commonly known as "M Block" or simply M, though its name shows up on the actual game as 'M .
The first glitched block in its name seems to change according to whichever pokemon (or trainer) is in the left corner of the screen.

This Pokemon seems to more commonly appear at level 80 or zero, and is almost identical to MissingNo. except for when you try to catch it.

When attempting to capture M it is recommend that you have two empty slots in your party. After you throw a Pokeball at M and capture it, you will remain in battle and therefore be able to capture it AGAIN. This second M will register as a DITTO if caught. If you catch the Ditto or not, not having an extra slot in your party (and sending M to the PC) will make your game a lot more likely to freeze, and you may have trouble withdrawing it from the PC.
It can also be noted that if M gets any experience points it will grow to level 100 and evolve into a Kangaskahn.

Encountering MissingNo. in the Red and Blue versions has a few notable side effects which one should take heed of:

Duplication of the item in your 6th slot
Whichever item you have in the 6th slot will be duplicated to 100+ of that item in both methods. It should be noted that you should MAKE ABSOLUTE SURE that you do not have a "key item" (an item the game will not let you delete) in the 6th slot, because this can eventually lead to your entire bag being filled with something like Town Maps, causing you to be unable to carry any other items.

Your hall of fame on the PC will be glitched up
(assuming you have beat the Elite Four already).
This is actually very interesting, as you can see many Pokemon you don't own, weird symbols and strange music. If you beat the Elite Four again after glitching your hall of fame, the newest hall of fame entry will not be glitched up unless you fight MissingNo. again. The glitches you will see hall of fame seem to change on their own at times, but they will change almost completely if you fight another MissingNo. Once you glitch a hall of fame entry, it will never go away.

Graphics Glitches
This one will only happen if you actually CATCH MissingNo. The graphics of your Pokemon and Pokemon that you fight in battle will be reversed and glitched up whenever they attack. This effect is not permanent and should only last about 10-15 minutes before going away on it's own. Sometimes it may come back but it should always go away by itself.

Changing into Rhydon
Sometimes when you catch MissingNo. it will randomly turn into a Rhydon. (If I remember correctly it happens more commonly if you deposit your MissingNo. into the PC.)

What Makes it Possible

When performing the Cinnabar Island trick, people may not get the same results as other people. This is because how how the trick works in the first place, which is mostly a screw up in the programming on GAMEFREAK's part.

When the programmers were creating the map to determine which Pokemon appear in which area, they programmed the 'half land half water' edge of Cinnabar as a place that wild Pokemon could appear, but they forgot to define which Pokemon appeared there. This usually wouldn't be a big deal because it would just use the settings from the patch of grass you were in previously.

However... When you talk to the Old Man who catches Weedle, the variables assigned to "Your Name" are overwritten with "Old Man" when it says "Old Man threw Pokeball!"

But what does this have to do with anything?
Well, when the variables that make up your name are overwritten, they had to decide on a place for the variables for "Your Name" to go, so the game could recall them later. It just so happens that the programmers had the variables for "Your Name" overwrite the slots for what Pokemon you can run into, since when you went into a new area they would be re-written, and wouldn't disturb the game. Because of this, you can run into MissingNo. and other level 100+ Pokemon on the edge of Cinnabar.

Determining Which Pokemon

The letters 2, 4, and 6 of your name will determine the levels of the Pokemon you can run into. First, take the NUMERICAL equivalent (A=1, B=2, etc.) of those letters, and add 127 for uppercase or 159 for lowercase. In addition, the symbols are as follows:

Also, at the end of your name, the game inserts an 80 (HEX 50) to designate "End of Name". Because of how the variables are used, this means that one of the levels your MissingNo. (or 'M ) will be is always Level 80.

While it is determined by name, the lowest number assigned to a character (other than the 80 that is assigned to the "End of Name" character) is 128, for a capital A. The low numbers like 21 represent glitch characters that are not available for naming anything and can only be found with a cheat device.

For convenience, here is the table of what Pokemon will appear for each letter. Letters 3, 5, and 7 are used to determine this:

Using this as a reference, you can choose which Pokemon (or MissingNo.) will appear by changing your name when you start a new file accordingly. (I like to use the name "Tobias" in some of my games because both the letters "b" and "a" will give MissingNo.)

Be warned not to use any of the special characters in your name, however. In which case you may fight a trainer instead of a Pokemon. This is because trainer characters are stored as Pokemon data, though treated differently by the game. You will not be able to get out of the match, and eventually one of their Pokemon will be a glitch that can freeze your game. Also to keep in mind, species the third letter goes with level from the second, species from the fifth goes with level from the fourth, and species from the seventh goes with level from the sixth.

Mew Glitch

This method was originally posted on GameFAQs as a way of getting mew, though MissingNo. Can also be obtained though it. (I've tried to get into contact with the person who made the FAQ to get permission, but their e-mail dosen't work...so I apologize for that, but if you want to see the whole Mew FAQ you can, here.)

In order to do this you will need:
a Pokemon with FLY
a Master Ball (or possibly Ultra Balls)

In order for this to work, you must have at least one trainer who appears at the edge of the screen that you have NOT fought yet, the most commonly used being the Gambler that's facing the door to the underground path on route 8. (There are other trainers it works with, but this one is the easiest to explain.)

First, go near one of the trainers without them coming on screen and save. For this to work you position yourself so that the trainer you are about to use is one square off the screen, so that if you take one step you will see them.
For the gambler, stand right in front of the underground path entrance and then walk down . QUICKLY press start before the exclamation mark appears above his head.
After this, FLY to Lavender town and go into the Pokemon Tower. While there, fight a Channeler then leave. (Note: some of the Channelers will give you different Pokemon, I'm not 100% sure which ones will give you which Pokemon, but most should give you MissingNo.) Head back to the route where the gambler was, and the menu will pop up. When you press B to close it, a level 7 MissingNo. will appear.
It is very hard to catch, and I do not know if it is even possible to catch it with ultra balls (which is why I suggest you use a master ball... I am not even sure if it's possible to catch it without a master ball).

MissingNo. obtained using this method will always be on level 7. Unlike the MissingNo. obtained in the classic method, MissingNo. caught using the Mew Glitch will level up normally when they get any experience points.

Since the "classic method" of catching MissingNo. does not work in the yellow version, it was long believed that there was no way of encountering it. Upon the discovery of the Mew glitch it was realized that MissingNo. could in fact be caught in the Yellow version, too.

When catching MissingNo. in the yellow version, simply follow the same steps as you would when using the Mew glitch to get it in Red/Blue.

Side Effects

While you can catch MissingNo. using the same method as in Red/Blue, there are quite a few additional side effects.

Particularly Weird:
some REALLY weird stuff will happen to your game during and after you capture or encounter MissingNo. on the yellow version. Some of these are:

- When encountering MissingNo. in the yellow version, the screen will stay black for much longer than usual and often it will freeze. You may need to try several times before you get to fight it.

- The yellow version MissingNo. has no cry, and the battle music does not play when you fight it. You will hear no sounds unless your Pokemon's HP goes into the red.

- This MissingNo. does not look the same as the Red/Blue MissingNo.

- Instead of knowing two Water Gun's and Sky attack, this MissingNo. will know Bind, Pay Day, and Water Gun. (or sometimes just Water Gun and Pay Day)

- You may get various glitches with the pikachu sprite

- Sometimes, after you fight MissingNo. you will see sprites of Red walking ALL OVER the screen.

- Unlike in Red/Blue, if this MissingNo gets any exp it will revert to level 1, and require a glitched amount of exp to reach the next level

- Rather than being type1/Bird, this MissingNo. is type1/Normal while its type 2 is glitched blocks that change.

While this MissingNo. sometimes has no cry, at times it will have the cry of the red/blue MissingNo.
At other times, rather than there being no music playing when you battle it, you will hear some really weird and creepy "music" (I have a recorded of a clip of it, which you can listen to here)

I have not yet been successful in battling this MissingNo. on an emulated version, though I have come across even more weird stuff.

When first entering battle, it says MissingNo. learned an attack called "'v", and afterwards it keeps saying "Missingno is trying to learn" over and over again the only way I was able to get out of this was by resetting.
I did manage to take screen shots, though, which can be found on the screen shots page.

While MissingNo. is considered to be a glitch Pokemon, it is still able to be traded to other versions of the game...though sometimes with even stranger side effects.

Red/Blue to Red/Blue
Trading a MissingNo. between red/blue versions is not likely to have any problems, and neither will battling for the most part. While the graphics glitches from encoutering MissingNo. will still be seen (if they haven't already gone away) on your screen, your opponent's will be fine and MissingNo. will behave as a normal Pokemon in battle.

Red/Blue to Yellow
Here's where some weird stuff starts to happen... If you trade your Red/Blue MissingNo. to the Yellow version, it will lose its "BIRD" type and its type will change to Type1/Normal and the type 2 will usually have a glitched block or number 9.
Its stats will also have different glitched blocks mixed in with the numbers
To get even more weird though, if you trade the MissingNo. BACK to the red or blue version afterwords, depending on which MissingNo. it is, it may revert to level zero, and not only will the OT and OT number will change, but the MissingNo's name will change to "ISSINGNO."
One of my MissingNo. even had a different attack upon trading it back

English to Other Language Versions
Since the French, German etc. versions are apparently compatable with the US versions, MissingNo. can be traded to them.
This yeilds possibly less weirdness than the trades to yellow, but it will still drop the "BIRD" type.
After trading, if the MissingNo. gets any EXP. it will not go to level 100, but to level 94 for some reason. I also noticed that once when I sent it into battle it fell asleep for no reason.

Red/Blue to Crystal
While you can't actually trade your MissingNo. to the Crystal version from Red/Blue, you can view its status screen. If a trade is attempted, the Crystal version will get a message that says "Your friend's (pokemon) appears to be abnormal!" and it will auto-cancel the trade.
When viewing the stats of R/B MissingNo. on Crystal, they will appear as different Pokemon, for example: My 'M appeared as a Slowpoke, while my 'b' and 'a' MissingNo.'s appeared as Remoraid and Miltank.
Strangely, no matter what Pokemon your MissingNo. or M appears as, they seem to always be holding a CARBOS item.

MissingNo. Myths

Over the years I've heard and read a number of claims regarding MissingNo. that just don't have any basis in truth what so ever. They seem to be assumptions based only on a lot of "he said, she said" and have never happened to myself, or anyone that I know. Some false things about MissingNo. are:

"MissingNo. is Mew"
Um... no. Mew is already programmed into the game and there are ways that you can (or once could) get it legitimately. I don't know where this whole "MissingNo. is Mew" thing started in the first place, but it's pretty stupid.

"MissingNo. will erase your game"
Yeah, you're all gonna want to jump on me for this, but the truth is, MissingNo. CAN NOT ERASE YOUR GAME, assuming you used a non-cheat-device method of catching it. People seem to jump the gun when they see graphics glitches and then blame everything that happens to their games on MissingNo. The sad truth is: game files CAN become corrupted, and catching MissingNo. or not has NOTHING to do with it.
People also need to realize that these games are getting old, and while the batteries are SUPPOSED TO last a long time, many of them went dead way before they were supposed to, causing files to be erased and you being unable to save.

"MissingNo. can wreck your physical cart!(or GB)"
...This one is just ridiculous. Like the above, just another wild assumption with absolutely NO basis. I used to hear all the time that "it's safe to encounter MissingNo. on a gameboy pocket or color but not the original gameboy"...This is the biggest load of crap I've ever heard. For one thing, I caught MissingNo. all the time on my old clunky gameboy and not a thing happened. The claim that a MissingNo. can actually destroy your cartrige or gameboy is just ridiculous and NOT TRUE.

"When you encounter MissingNo., it writes to your save file!"
MISSINGNO. DOES. NOT. WRITE. TO. YOUR. SAVE. FILE.
People believe this because it says "saving" when encountering MissingNo on the stadium games.. HOWEVER.
Battles do not in any way, shape, or form, by any extent of coding error, NO MATTER WHAT, EVER WRITE TO SRAM. IT CAN'T DO THAT.
The battle engine, even if MissingNo. glitched the game to smitherines, could in no way access SRAM.
It is in an entirely different range of memory so that random events in game can not break it. The only way to access that part of the memory is through the save function which is programmed to access it when nothing else will effect it, hence the reason why you cant move, etc during saving.

MissingNo. are Missing Numbers

One of the most commonly held theories about MissingNo. seems to be that it is a "place holder" in the programming for spaces that they didn't use for Pokemon. This seems to be the most viable explanation for a few reasons:

In most Game Boy games, the fewest possibilities for a particular variable is 256. This starts at HEX 00 and ends at FF.

This is the same case in the early Pokemon games, but since there were only 151 Pokemon, not 256, they needed to have SOMETHING occupy the other 105 slots.

So looking at this, MissingNo. is present in the games because it had to be.

This would still leave open the possibility for there to have been Pokemon that they put in, but later removed, but the absence of any unused sprites makes this kind of unlikely. (Even ruby/sapphire had some unused sprites, while not of POKEMON!)

With this in mind, MissingNo. and M turn into Kangaskahn and Rhydon because they are so early in the hex listings in an attempt by the game to 'fix' what happened (since we were never meant to encounter MissingNo.... according to Nintendo)
You can see what I mean by the hex listings by looking at this screen shot from a hex editor.
As you can see, MissingNo. literally is a "MISSING NUMBER"